The broad objective is to explain differences in rates of Post-Traumatic Stress Disorder (PTSD) and comorbid disorders in U.S. Vietnam veterans from different social statuses indicated by gender, ethnic/racial background, and parental socioeconomic status (SES). The specific aims involve tests of alternative hypotheses about the primacy of exposure to environmental war- zone stressors, the role of antecedent personal predispositions, and the influence of endogenous cultural factors associated with the differing social statuses. The data for these tests come from the National Vietnam Veterans Readjustment Study (NVVRS). The NVVRS was conducted by the Research Triangle Institute (RTI) in response to a Congressional mandate to investigate PTSD and other psychological problems in the U.S. veterans. The study of nationwide samples of 3,016 Vietnam Theater veterans other Vietnam Era veterans, and non-veterans began in 1984, and the intensive data collection continued over the next several years. The veteran samples were drawn from military records and interviewed in detail about their premilitary lives, their military experiences, and their lives following the war as well as a wide variety of psychological symptoms and problems. In addition, a subsample of respondents consisting of 343 Theater veterans and 93 Era veterans were given intensive research diagnostic examinations by experienced clinicians. These subsample diagnoses contain the only data in the study on onset and course of PTSD, and reports of results of the study thus far have focused on current PTSD in the larger samples. The rate of current PTSD (present 15 to 20 years after the war) was 15.2 percent in male Theater veterans, six times as high as for the Era comparison sample. This rate of persistent or recurrent PTSD was especially high in Hispanics (27.9 percent) and African-Americans (20.6 percent) compared to nonHispanic whites (13.7 percent). These ethnic/racial differences are reduced but do not disappear when parental socioeconomic status (SES) is controlled. Among female Theater veterans, mainly nonHispanic white nurses, the 8.5 percent rate of current PTSD is substantially lower than for males. Very large majorities of both male and female Theater veterans with current PTSD were diagnosed with other concomitant psychiatric disorders. The reasons for these gender and racial/ethnic differences are unknown. The proposed study will focus almost exclusively on the diagnosed subsample in order to investigate alternative explanations of the group differences as the hypotheses apply to initial onset and to course of PTSD and comorbid disorders. Plans are set forth for utilizing existing measures and developing new ones necessary for the task from the NVVRS data, and for a variety of statistical analyses using descriptive statistics, graphical methods, and logistic and Gaussian multivariate regression. The long term goal is to increase knowledge of how humans adapt or fail to adapt to adversity and stress, and to contribute to the account of an historic event in the life of this nation.